HYDROGENATION OF ARENES WITH METALLIC IRIDIUM AND RHODIUM POWDERS PREPARED FROM IRIDIUM(I) AND RHODIUM(I)-COD COMPLEXES UNDER MILD CONDITIONS

Metallic iridium and rhodium powders prepared from the reactions of [M (COD)(PhCN)(2)]ClO4 (M=Ir(1), Rh(2); COD=1,5-cyclooctadiene) with hydr ogen at room temperature in methylene chloride show catalytic activiti es for hydrogenation of arenes at room temperature under atmospheric p ressure of hydrogen. Most substituents (CH3, COOH, NO2, CH2OH4 CHO, OP h, OCH3, C=C, halogens and CH2Cl) on aromatic ring suppress the rate o f the hydrogenation of the aromatic ring while the aromatic ring hydro genation of phenol and 1,4-dihydroxobenzene is faster than that of ben zene over these metallic powders. Hydrogenation of benzoic acid occurs only at the aromatic ring leaving the COOH group intact over iridium metal powders while benzoic acid is not hydrogenated at all over rhodi um metal powders. Carbonyl, nitro, acetylenic and olefinic groups on a n aromatic ring are hydrogenated prior to the aromatic ring hydrogenat ion. Hydrogenolysis of OH groups of phenol, benzyl alcohol and 1,4-dih ydroxobenzene, and hydrodehalogenation of halobenzenes, benzyl halides and cinnamyl chloride also occur along with the hydrogenation of arom atic ring.